Apparatus and process for the production of fire-refined blister copper

ABSTRACT

Fire-refined blister copper is produced from copper concentrate by a process comprising: 
     A. melting and oxidizing the copper concentrate in a smelting furnace to produce molten matte and slag, and to separate one from the other; 
     B. removing the molten matte from the smelting furnace; 
     C. solidifying the molten matte; 
     D. injecting the solidified matte into a converting furnace in which the matte is converted to blister copper and slag; and 
     E. transfering the blister copper from the converting furnace to an anode furnace to produce fire-refined blister copper. 
     After the fire-refined blister copper is produced in the anode furnace, it is typically transferred to an anode casting wheel on which it is converted to copper anodes suitable for subsequent electrolytic refining to cathode copper.

FIELD OF THE INVENTION

This invention relates to the pyrometallurgy of copper. In one aspect,this invention relates to the smelting of copper concentrates to producefire-refined blister copper while in another aspect, this inventionrelates to a copper smelting apparatus and process that allows theuncoupling, in both space and time, of the smelting and convertingfurnaces and their respective operations. In another aspect, thisinvention relates to a process for the smelting of copper that is bothenergy efficient and that has a very low impact on the environment.

BACKGROUND

Copper smelting involves two primary process steps: (1) smelting toproduce copper matte, and (2) converting to produce copper metal. Whilesmelting technology has changed dramatically in the last thirty years,converting has changed little since Messrs. Peirce and Smith developedthe side blown converter in the early 1900's. Although the Peirce-Smithconverter has proven its worth over time, its design does not lenditself well to compliance with the ever increasingly stringentenvironmental requirements that copper producers must meet. This is dueprimarily to processing liquid matte, slag and metal in multiplevessels, and transferring each from one vessel to another by use ofladles and overhead bridge cranes.

In the late 1970's, Kennecott Corporation began an investigation ofalternatives to Peirce-Smith with copper converting, and one result ofits efforts was U.S. Pat. No. 4,416,690. According to the process ofthis patent, solid matte particles are fed to a converting vessel withoxygen and flux in such a manner that the converting reaction isconducted autogenously and with the evolution of substantially undilutedsulfur dioxide gas (which can be captured and used in the production ofelemental sulfur or sulfuric acid). This converting process eliminatesthe need for the transferring of liquid matte from the smelting furnaceto the converting furnace, and the concomitant fugitive gas emissions.The process is known as solid matte oxygen converting.

Mitsubishi Materials Corporation teaches in U.S. Pat. No. 5,205,859 anapparatus and process for the continuous smelting of copper. In thisprocess, copper concentrate is melted and oxidized in a smelting furnaceto produce liquid matte and slag, and then both are transferred to aseparating furnace in which one is separated from the other. The liquidmatte is transferred to a converting furnace in which it is converted toblister copper, and the blister copper is then transferred to aplurality of anode furnaces for further fire refining. The transfer ofproduct from one furnace to another is accomplished by a series oflaunders and since the entire process is continuous, balanced productionand transfer must be maintained to keep the process operational.

While the Mitsubishi and various other processes known and in use todayall produce copper, to one degree of efficiency or another, all aresubject to improvement, particularly with respect to environmentalefficiency. The reality of today is that not only must the copperproducer be cost efficient, but it must also be environmentallyefficient. Not surprisingly, a continued interest exists in thedevelopment of copper producing technology that accomplishes both theseends.

SUMMARY OF THE INVENTION

According to this invention, fire-refined blister copper is producedfrom copper concentrate by a process comprising:

A. melting and oxidizing the copper concentrate in a smelting furnace toproduce molten matte and slag;

B. removing the molten matte and slag from the smelting furnace inseparate streams;

C. solidifying the molten matte;

D. feeding the solidified matte into a converting furnace in which thematte is converted to blister copper and slag; and

E. transferring the blister copper from the converting furnace to ananode furnace to produce fire-refined blister copper.

After the fire-refined blister copper is produced in the anode furnace,it is typically transferred to an anode casting device, typically ahorizontal casting wheel, on which it is converted to copper anodessuitable for subsequent electrolytic refining to cathode copper.

In a preferred embodiment of this invention, the smelting and convertingfurnaces are flash furnaces, and the converting step is solid matteoxygen converting as described in U.S. Pat. No. 4,416,690. In this andother embodiments, the molten matte is transferred from the smeltingfurnace to a solidification apparatus, e.g. granulating or castingequipment, and the solidified product is either transferred to theconverting furnace, with or without prior size reduction, or is stored.This uncoupling of the smelting and converting furnaces allows virtuallycomplete flexibility in scheduling their respective uses, and allows oneto be physically remote (e.g. off-site) from the other.

In other preferred embodiments of this invention, the blister copper istransferred from the converting furnace to a series of anode furnacesthat are operated such that the converting furnace can maintaincontinual operation. The blister copper is typically transferred fromthe converting furnace to the anode furnaces by an arrangement oflaunders in combination with a molten metal divertor. In certainembodiments, a holding furnace is positioned between the convertingfurnace and the anode furnaces to receive, hold and in somecircumstances, process, the blister copper prior to its transfer to theanode furnaces.

In another embodiment of this invention, the twin rotating anodefurnaces are replaced with a single, non-rotating furnace. In thisembodiment, the furnace is sized to process in a like amount of time theequivalent of the twin rotating furnaces operated in tandem, and thefurnace is designed with separate oxidizing and reduction zones in fluidcommunication with one another that are operated continuously andsimultaneously.

The process of this invention is environmentally efficient. In certainembodiments, copper concentrate can be converted to fire-refined blistercopper with capture of at least about 98 percent, preferably at leastabout 99 percent, of the input sulfur, and sulfur dioxide emissions canbe reduced to less than about 5, preferably less than about 3, kilogramsper metric ton of copper produced. By "capture" is meant that the inputsulfur, i.e. the sulfur value of the copper concentrate, is retained inthe process or leaves the process as a product or by-product, e.g. ametal sulfide, sulfuric acid, etc. In addition, particulate and acidmist emissions are significantly reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic flow diagram of one embodiment of this invention.

FIG. 2 is a side, cut-away view of a flash smelting furnace.

FIG. 3 is a side view of a continuous blister tapper.

FIG. 4a is a side view of a launder arrangement in combination with adivertor.

FIG. 4b is a top view of the launder arrangement and divertor of FIG.4a.

FIG. 5 is a side view of a nonrotary anode furnace.

DETAILED DESCRIPTION OF THE INVENTION

The copper concentrates used in the practice of this invention can beprepared by any conventional process, and typically contain betweenabout 10 and 50, preferably between about 20 and 40, percent by weightcopper. The concentrates contain other metals, e.g. iron, lead, bismuth,arsenic, molybdenum, one or more precious metals. etc., that areassociated with the copper in the ore deposit, and these metals, as wellas the copper, are present in the concentrate principally as sulfides.The concentrate is preferably in particulate form, typically with anaverage particle size less than about 65 U.S. mesh.

Smelting furnaces are available in a number of different designs, butare basically of two kinds: melt and oxidative. The former are designedmore to melt than oxidize the concentrate, and thus they produce alow-grade matte, e.g. a matte with a copper concentration between about30 and 50 percent by weight. Since the use of a high-grade matte, e.g. amatte with a copper concentration above 50, preferably between 60 and80, percent by weight, is preferred in the converting step of thisinvention, melt-type smelting furnaces are not favored for use in thepractice of this invention.

Oxidative-type smelting furnaces are also of two basic designs, bath andflash, and either design can be used in the practice of this invention.Both designs are well known in the copper smelting industry.Representative bath smelters include those operated by Noranda Inc. atits Horne, Canada facility; Mitsubishi Materials Corporation at itsNaoshima, Japan facility; and Isamelt at its Mt. Isa, Australiafacility. Representative flash smelters include those operated byOutokumpu Oy at its Harjavalta, Finland facility, and Inco Limited atits Sudbury, Canada facility. Because flash smelting furnaces can beoperated in a manner more consistent with existing and foreseeableenvironmental regulations than bath smelting furnaces (they are morereadily sealed against fugitive gas and particulate emissions than bathfurnaces), flash smelting furnaces are the preferred smelting furnacesfor use in this invention. Outokumpu flash smelting furnaces areparticularly preferred.

The copper concentrate is fed to the smelting furnace in conventionalfashion. If the furnace is a flash smelting furnace, then theconcentrate is mixed with flux and optionally recycled converter slagand/or slag concentrate (all of appropriate size), and the mix is thendried and fed (e.g. blown) into the furnace with oxygen oroxygen-enriched air. In certain embodiments of this invention, theconcentrate and other feed components to the flash furnace are reducedto fine particle size by any conventional technique, e.g. ballmill orvertical roller grinding. The furnace is operated in conventionalfashion, and the concentrate is transformed into an essentiallyquiescent pool of molten matte and slag within the confines of thefurnace. The matte and slag are allowed to separate within the furnace(slag floats to the top of the matte because it is less dense than thematte), and the molten matte and slag are removed separately. The slagis removed from the furnace by skimming it from the surface of the mattethrough one or more appropriately located tap holes or skimbay openingsin one or more walls of the furnace. It is collected in a conventionaltransport vessel, and then it is removed from the furnace site forfurther processing or disposal. The molten matte is drained from thefurnace through one or more appropriately located tap holes (usuallydifferent from those used to remove the slag), in one or more walls ofthe furnace, and then solidified.

Any process and apparatus that will solidify molten matte can be used inthe practice of this invention. These processes include water and airgranulation, casting, and a cooled vibrating plate. Casting is notfavored because it produces large masses or chunks (e.g. an average sizemeasured in inches or feet) of matte which in turn usually require moreprocessing, e.g. grinding, before use as a feed to the convertingfurnace, and it is slow (cooling can take minutes to hours, dependingupon the size of the casting). Moreover, this solidification process isdifficult to control environmentally (it produces considerable fugitivegases, particularly if artificial means of cooling are employed, such asforced air or water spray).

The cooled, vibrating plate process, i.e. the process in which moltenmatte is fed or dropped onto a cooled and vibrating plate on which itquickly solidifies and eventually falls into a storage area or onto atransfer vessel, is also not favored because it too produces relativelylarge chunks, e.g. disk-shaped chunks in excess of 6 inches in diameter,and these too are relatively slow (e.g. tens of seconds) to cool to anambient temperature.

While air granulation is quick and produces small particles relative tocasting and the vibrating plate, this too is a less preferred process ofsolidifying the molten matte because the sulfur and iron values in thematte readily react with the oxygen in the air, and this can causepollution problems. Volitile heavy metals such as lead, arsenic andcadmium can also be liberated and once liberated, these become adifficult enviromental control problem. As such, air granulation usuallyrequires pollution control equipment not otherwise needed in other formsof molten matte solidification.

One variation on air granulation is the use of an inert gas, e.g.nitrogen, to avoid the oxidation of the sulfur values in the matte.However, this process is cumbersome and expensive in terms of alarge-scale commercial smelting operation.

The preferred process of molten matte solidification is watergranulation. Two preferred water granulation techniques are water sprayand mechanical dispersion. In the water spray technique, molten matte issimply poured through a spray or curtain of water (typically under high,e.g. about 20 to about 150 psi, pressure) which results in a rapidquench of the matte and the formation of small, sand-like granules. Thegranules or particles are cool to the touch within a few tenths of asecond of formation, and little, if any, fugitive gases, volitile heavymetals, or particulate matter is created.

Mechanical dispersion also produces small, sand-like granules that arecool to the touch within a few tenths of a second of formation and withlittle, if any, formation of fugitive gases, heavy metals or particles,but this technique requires more in terms of apparatus. However, thegranules produced by this process tend to be coarser than those producedby the water spray technique, and thus tend to contain less moisture(which means that particles made by this technique require less dryingbefore undergoing downstream processing).

Regardless of the process used to solidify the molten matte, preferablythe solidified matte is subjected to a size reduction step before it isfed to the converting furnace. The solidified matte can be reduced insize by any conventional technique, e.g. verticle roller mills orair-swept ball mills. With respect for use as a feedstock to a flashconverting furnace, preferably the matte is reduced to an averageparticle size of less than about 65 mesh (U.S. Standard), but largerparticle sizes can be used, e.g. about 0.2-2.0 mm.

Copper matte, flux, and optionally, dust from any of the various matteprocessing steps, are fed to a converting furnace in any conventionalmanner. Converting furnaces are basically of two types, flash (alsoknown as suspension) and bath, and the purpose of both furnaces is tooxidize, i.e. convert, the metal sulfides to metal oxides.Representative bath furnaces include those used by Noranda Inc. at itsHorne, Canada facility, and Inco Limited at its Sudbury, Canadafacility. Representative flash converting furnaces include those used byOutokumpu Oy at its Harjavalta, Finland facility, and the KHD ContopCyclone furnace used by Asarco at its El Paso, Tex. facility. TheOutokumpu flash converting furnace is a preferred converting furnace foruse in the process of this invention. The converting step raises thecopper concentration in the matte from 50-80 percent by weight to about98 plus percent by weight.

While the copper matte can be fed to the converting furnace in anysuitable manner, in the preferred embodiment (in which the furnace is aflash converting furnace) the matte is fed as a dry, finely dividedparticulate (150 U.S. mesh/P₈₀ or in other words, eighty percent of theparticles will pass through a 150 U.S. mesh sieve). Preferably, thefurnace is operated such that the matte is converted to blister copperusing the solid matte oxygen conversion process taught in U.S. Pat. No.4,416,690 (which is incorporated herein by reference). According to thisprocess matte, oxygen and flux are fed into the furnace such that theconverting reaction is conducted autogenously (although small amounts ofvarious fuels can be burned to provide auxiliary heat to the reactionfor purposes of exercising tight furnace control). Molten blister copperaccumulates within the furnace, and the slag accumulates on the top ofthe molten copper. Preferably, the flash converting furnace is operatedon a continuous basis.

While the slag is separated from the blister copper in a manner similarto that in which it is separated from the matte in the smelting flashfurnace, the removal of the blister copper from the flash furnace ispreferably accomplished through the use of a continuous blister tapper(CBT) as opposed to one or more tap holes (although these can be used ifdesired). The design and operation of the CBT can vary to convenience,but preferably it is attached to the furnace in such a manner that theblister is continuously transferred from the furnace to the CBT whilethe slag is retained in the furnace.

In one embodiment of this invention, the blister copper is transferredfrom the converting furnace, preferably through a CBT, to a holdingfurnace. The primary purpose of this furnace is to provide schedulingflexibility to the overall smelting process, i.e. to provide a locationfor the accumulation of molten blister if the anode furnaces cannotaccept it for any reason directly from the converter. However in certainembodiments of this invention, the holding furnace can be adapted to notonly hold the molten blister, but also to further process it prior toits introduction into an anode furnace.

In a typical and preferred embodiment of this invention, two rotatinganode furnaces are located proximate to the converting or holdingfurnace, as the case may be, and are sized to accommodate the outputfrom the converting and/or holding furnace. These furnaces are typicallyof conventional design and operation, and are used in tandem with oneanother such that while one is fire-refining the blister to anodecopper, the other is filling. The output from the anode furnaces istransferred to an anode casting device (of any conventional design) onwhich the anodes are formed and subsequently removed to electrolyticrefining. The copper concentration in the anode copper is 98 pluspercent.

In another embodiment of this invention, a single anode furnace, eitherrotating or nonrotating, is located proximate to the converting orholding furnace, as the case may be, and is sized to accommodate theoutput from the converting and/or holding furnace. This nonrotatingfurnace can be of any suitable configuration, and consists of anoxidation zone and a reduction zone. These zones are separated by anyconventional means, e.g. a dam or baffle, but are otherwise in fluidcommunication with one another such that the oxidized blister can movefreely and continually from the oxidation zone to the reduction zone.

.Iadd.In a preferred embodiment of this invention,.Iaddend..[.B.]..Iadd.b.Iaddend.lister copper is transferred from theconverting furnace to the anode furnace by a series of refractory-lined,hooded launders that converge at a molten metal divertor which, in turn,directs or diverts the blister to one of the anode furnaces. If thesmelting and converting process train includes only one anode furnace,then a divertor is not needed and the blister can be laundered directlyfrom the converting furnace to the anode furnace. The divertor can be ofany suitable shape and design although a shallow dish shape with apouring lip is a preferred design. The divertor is sized to accommodatecontinuous transfer of blister from the converting furnace to the anodefurnaces; it is refractory-lined and hooded (like the launders); it isequipped with a burner to keep the blister molten; and it is rotablymounted such that it can direct the output from the converter to theopen anode furnace. If a holding furnace is positioned between theconverter and the anode furnaces, then it is positioned between theconverting furnace and the divertor. Preferably, the launders anddivertor are arranged such that the blister moves through the systemunder the force of gravity.

Various embodiments of the invention are further described in thedrawings in which like numerals are employed to designate like parts.Although items of equipment, such as valves, fittings, pumps,condensers, holding tanks, pipes, and the like, have been omitted so asto simply the description, those skilled in the art will recognize thatsuch conventional equipment can be employed as desired.

FIG. 1 is a schematic flow diagram of one preferred embodiment of thisinvention. Copper concentrate is transferred by any conventional means(not shown) from storage area 10 to concentrate hoppers 11a and 11b forblending with slag or slag concentrate and flux which are held in slaghopper 12a and flux hopper 12b. The flux (typically metallurgical gradesilica, i.e. silicon dioxide) is acquired from any convenient source,and the slag is typically a blend of converting furnace slag andsmelting furnace slag concentrate (the latter a product of flotation toincrease its copper content). All are sized and blended for optimumoperation of the smelting furnace. These feeds can be sized eitherbefore or after blending with one another, although typically thesizing, if required at all, is performed prior to blending (the flux andslag components of the blend are usually considerably more coarse thanthe copper concentrate component). The respective amounts ofconcentrate, flux and slag/slag concentrate in the smelting furnace feedwill vary with, among other things, the nature of the concentrate and incertain embodiments and for various reasons, neither slag nor slagconcentrate is a component of the feed.

After the concentrate, flux and if present, converter slag are blendedwith one another (by means not shown), the blend is transferred byconveyor 13 to dryer 14 in which the moisture content of the blend isreduced from typically about 8-10 percent, based on the weight of theblend, to typically less than about 0.5 percent. Dryer 14 is a rotatingdrier drum, typically gas-fired, positioned such that it is at a slightangle with the ground. The blend enters dryer 14 at its elevated end,travels the length of the dryer under the force of gravity and under ablanket of nitrogen (to minimize oxidation), and exits the dryer at itslower end into dryer bin 15. The operating conditions of dryer 14 willvary with a host of variables, but typically the blend will be exposedto temperatures in excess of 100° C. for ten or more than minutes. Thedried blend is then pneumatically transferred from dryer bin 15 tosingle, dual-hopper feed bin 16 using high density pneumatic conveyingequipment, such as that available from Paul Wurth S. A. of Belgium. Frombin 16, the blend is then fed into flash smelting furnace 17. Dust andgases from dryer 14 and bin 15 are gathered and transferred by means notshown to electrostatic precipitator 18 and other cleaning equipment notshown for collection and ultimate return to the smelting process.

The design of the flash smelting furnace can vary, and those describedin U.S. Pat. Nos. 3,900,310, 4,169,725, 4,599,108 and 5,181,955 (all ofwhich are incorporated herein by reference) are illustrative. Typicallyand as shown in FIG. 2, the furnace comprises reaction shaft 19, lowerfurnace 20, and uptake shaft 21. The furnace is equipped withconcentrate burner 22 and extensive water cooling (not shown) to prolongthe useful life of the furnace. The dried blend and oxygen (oroxygen-enriched air) are fed to the burner in such a manner that theconcentrate is smelted to matte and slag both of which accumulate intoan essentially quiescent pool in lower furnace 20. Since the slag isless dense than the matte, it rises to the surface of the pool and isperiodically removed from the furnace by any conventional technique(e.g. skimming through one or more slag tap holes not shown). Thecollected slag is then cooled, crushed, and then typically ground andfloated to produce a copper concentrate suitable for recycling tosmelter furnace 17. If the slag is not to be recycled for any reason,e.g. an undesirable metal composition, insufficient furnace capacity,etc., then other disposal options are available, e.g. sale to slagprocessors for extraction of residual metal values, land fill, and thelike.

Furnace 17 is sealed in a gas-tight manner such that the hot fugitivegases, e.g. sulfur, carbon and nitrogen oxides, water vapor, etc.,produced by the smelting process are retained in and channeled throughthe furnace to uptake shaft 21 in which the gases are collected and fromwhich the gases are discharged to waste heat boiler 23a (FIG. 1) throughmeans not shown. In waste heat boiler 23a (examples of which are thosebuilt and marketed by Ahlstrom of Finland), the majority of the latentheat value of the gases is captured and return to various points withinthe process. The heat-extracted gas is then transferred by means notshown to hot electrostatic precipitator 24a (examples of which are thosebuilt and marketed by ABB Flakt of Sweden).

The smelting of copper concentrates creates considerable amounts of dust(which comprises a wide range of materials including unsmelted orpartially reacted concentrate and flux, matte, various metal valuesincluding copper and precious metals, and the like) and forenvironmentally sound operation, this dust must be captured and eitherreturned to the process or otherwise appropriately disposed. Since thedust contains considerable metal value, especially copper and preciousmetals, preferably it is collected and returned to smelting furnace 17.Much (e.g. 60-70 percent) of the dust that is emitted from smeltingfurnace 17 is captured in waste heat boiler 23a, and the vast majority(e.g. 99 plus percent) of the dust not captured in the waste heat boileris captured in hot electrostatic precipitator 24a. The gases leavingprecipitator 24a and those leaving precipitator 24b are cleanedseparately (by means not shown, e.g. a wet scrubber), and then thesecleaned gases are combined (by means not shown) for further cleaning in,for example, another wet scrubber and/or a wet electrostatic mistprecipitator (also not shown) to remove quantitatively any residual dustprior to the gases entering acid plant 25.

The dust collected from waste heat boiler 23a and hot electrostaticprecipitator 24a is transferred to collection hopper 26, and from hereto smelter dust bin 27 for subsequent charging to furnace 17. In certainembodiments of this invention, some of the dust collected in hopper 26can be transferred to hydrometallurgical facility 28 for furtherprocessing, i.e. for recovery of various metal values such as bismuth,copper, lead, arsenic, antimony, and the like. The timing of thetransfer and the amount of dust actually transferred, if any, tohydrometallurgical facility 28 is dependent upon a number of differentfactors not the least of which is the metal composition of the dust, themetal composition of the concentrate feed to smelting furnace 17, andthe operating parameters of the smelting furnace. Dust is conveyedthroughout the overall process by pneumatic means (not shown).

The scrubbed gases are transferred to acid plant 25 for recovery ofmarketable sulfuric acid. Flash smelting furnace 17 is operated atconditions which generate concentrated sulfur oxide gas (relative tobath smelters and typically of 30-40 percent strength), and in turnthese gases lend themselves well to the efficient and quantitativerecovery of commercial sulfuric acid from their sulfur content. In apreferred embodiment of this invention, the acid plant is designed notonly to emit very low levels of sulfur dioxide (e.g. less than 100 ppmvSO₂), but also to produce steam as a by-product. In this preferredembodiment, the clean gas is diluted with air to 14% SO₂, and thenconverted to sulfuric acid. As such, these gases leave the overallsmelting process as a marketable product as opposed to undesired stackemissions.

The latent heat value of the fugitive gases from smelting furnace 17that is recovered in waste heat boiler 23a is transferred to power plant29 which generates power for use in the overall smelting process. In apreferred operation of this invention, the overall process includingcapture of heat values from the acid plant) will generate in excess ofeighty percent of its own energy requirements. This results in a majorreduction in the energy required from conventional fossil fuels (ascompared to most conventional copper smelting processes in operationtoday), and thus a major reduction in the environmental impact thatnecessarily flows from the consumption of fossil fuels.

Matte is withdrawn from furnace 17 through one or more matte tap holes(not shown), and transferred by enclosed launder (not shown) tohigh-pressure water matte granulator 30. Granulator 30 is preferably ofthe design as that used in the pyrometallurgy of nickel at the OutokumpuMetals OY smelter at Harjavalta, Finland, and is sized consistent withthe output of the smelting furnace. This apparatus is also designed foran essentially quantitative capture of any fugitive dust and gases thatmay be emitted from the granulation process. The granulated matteproduced by the process is sand-like in appearance (e.g. between about0.2 mm and 2 mm in size), and contains about 4 to 8 percent moisture.

One of the hallmarks of the pyrometallurgy of this process is theseparation of the smelting and converting steps in both space and time.The matte, once granulated and cooled, can be converted immediately orstored or shipped for future consumption. If the downstream operationsof the process are out of service for any reason, e.g. maintenance,upset, inadequate capacity, etc., the matte can simply be stored in anyconventional manner in matte storage facility 31 until needed. In thealternative, the matte can be shipped to another site for conversion toblister copper. In any event, this separation of smelting and convertingsteps eliminates the need to transfer liquid matte from the smeltingfurnace to the converting furnace, which in turn eliminates a majorsource of potential gas emissions and the ripple effect inherent withany continuous process (i.e. a problem in one part of the processaffecting all parts of the process).

In the preferred operation of the process of this invention, sufficientmatte is stored to provide the smelter with at least several days offeed. Matte is transferred from storage facility 31 by any suitablemeans (not shown), e.g. conveyor, land vehicles, etc., to matte grindingstation 32 at which it is reduced to an optimum size (e.g. to an averagearticle size of less than about 65 U.S. Standard mesh) for conversion inflash converter furnace 33. As noted above, the size reduction can beaccomplished by any conventional technology, but vertical roller mills,such as those available from Loesche, are preferred.

After suitable size reduction, preferably to a dust-like appearance, thematte is pneumatically conveyed by high density technology to flashconverter furnace 33 by way of baghouse 34 in which fugitive dust (i.e.matte) is captured and transferred by means not shown to dust hopper 35.The matte is collected from baghouse 34 into transfer hopper 36,pneumatically transferred to matte feed hopper 37, passed through weighcell 38, blended with dust and flux from hoppers 35 and 39,respectively, and then fed to flash converter furnace 33. The matte hasan average particle size of less than about 65 U.S. Standard mesh, thedust has an average particle size less than about 100 U.S. Standardmesh, and the lime-based flux has an average particle size of less thanabout 6 U.S. Standard mesh.

Flash converting furnace 33 is a smaller version of flash smeltingfurnace 17 except that the former has more extensive water and aircooling (not shown) than the latter. It operates in much the same manneras the flash smelting furnace. Matte, flux, dust and O₂ -enriched airare fed to the single matte burner in such a manner that upon ignition,the matte is converted autogenously (as taught in U.S. Pat. No.4,416,690). Supplemental heat can be employed for furnace controlpurposes as desired. As in the flash smelting furnace, the resultingblister copper and slag are collected in the lower furnace in anessentially quiescent pool, and dust-laddened gases are channeled to theuptake shaft for transfer to waste heat boiler 23b. These transferredgases are processed in the same manner as the gases transferred fromflash smelting furnace 17 to waste heat boiler 23a, and ultimately thesetwo gas streams are combined for cleaning in the wet scrubbers and/orelectrostatic mist precipitators prior to processing in acid plant 25.However, the dust captured from the gas stream discharged from flashconverter furnace 33 may be recycled back to furnace 33 by means notshown.

Converter slag is removed from furnace 33 in a manner similar to theremoval of smelter slag from furnace 17, i.e. the slag is skimmed fromthe surface of the blister copper and is discharged from the furnacethrough one or more slag tap holes. However, unlike the smelter slagprocessing procedure of collection in pots, cooling, and flotation, theconverter slag is transferred by way of heated, covered launders (notshown) to high pressure water slag granulator 40 (similar in mostrespects to matte granulator 30). The slag is reduced to a sand-likeconsistency, and recycled to the flash smelting furnace by means notshown.

Blister copper can be removed from flash converting furnace 33 by anysuitable means, but preferably the furnace is equipped with a heatedforehearth or CBT (FIG. 3) from which blister copper can be continuouslywithdrawn. In this embodiment, the CBT and lower furnace are in fluidcommunication with one another by means of a passage through whichblister copper can continuously pass from the lower furnace to the CBT.The passage is designed such that slag will not enter the CBT, and thefurnace and CBT are operated in such a manner that the blister copper isnot allowed to solidify within the passage or CBT. Typically the blistercopper is kept in a molten state while in the CBT by means of one ormore burners located above the CBT.

In a one embodiment of this invention, the blister copper is kept in amolten state through the use of an induction furnace as described inFIG. 3. In this embodiment, lower furnace 41 of a flash converterfurnace is in open fluid communication with CBT 42 by means of furnacetaphole 43 which is preferably located at or near the lowest part of thelower furnace end wall. Taphole 43 is designed and located in thefurnace end wall and the flash converter furnace is operated in such amanner that slag does not enter taphole 43. In the usual convertingoperation, the flow of blister copper from lower furnace 41 throughtaphole 43 into CBT 42, and eventually through CBT overflow 44 intolaunder 45, is continuous and as such, the continuous motion of theblister copper, in combination with heat imparted from burners (notshown) located above the CBT, retards any tendency for it to solidify.

In those circumstances, however, in which the continuous flow of blistercopper is stopped, then the copper has a tendency to solidify (which isgenerally undesirable because before continuous operation can beresumed, the solidified blister must either be physically removed orremelted, neither of which is an easy task). In a preferred embodimentof this invention, the blister copper is maintained in a molten statethrough the use of transformer 46 which is preferably a simple staticstep-down transformer, the secondary single-turn winding (not shown) ofwhich consists of a loop of the blister copper.

In operation, blister copper is heated through the action of transformer46 as it flows through taphole 44 into CBT 42. As a result, the blistercopper at the bottom of the CBT is hotter that the blister copper at thetop of the CBT, and this in turn imparts hydrostatic pressure,electrodynamic power and convection to the blister copper or in otherwords, this temperature difference imparts movement to the blistercopper within the CBT and taphole 43. This in turn, retards any tendencyfor the blister copper to solidify (both in the CBT and taphole 43),either when it is in continuous motion from lower furnace 41 to launder45, or when it is simply being held in the CBT. In addition, thisinduction heating minimizes or eliminates the need for the fuel-firedheating from burners located above the CBT, and this in turn minimizesfugitive gases and ventilation requirements for the CBT.

Blister copper can be removed from the CBT by any one of a number ofdifferent means, such as simple gravitational draining or natural orinduced overflow draining through one or more tapholes or overflowspouts. The former is simply the result of filling the CBT from thepower furnace until the blister reaches and moves through the taphole(s)or overflow spout(s). The latter requires pumping or elevating theblister to the taphole(s) or overflow spout(s) which are located abovethe top surface of the blister within the CBT in the absence of theinduced elevation. This pumping or elevating can be accomplished by anyone of several techniques.

In one technique, the bottom of the CBT is fitted with one or moreporous plugs through which an inert gas, e.g. nitrogen, is pumped. Thisgas swells the volume of blister copper within the CBT such that the topsurface of the blister is raised to or above a taphole or overflow spoutthrough which the blister can drain into a launder. In anothertechnique, the CBT is fitted with an induction pump which impartsconvection to the blister such that it is induced to "climb" aninduction conveyor or ladder to a taphole or overflow spout locatedabove the top surface of the blister. In both techniques, the need forexternal burners above the CBT is reduced or eliminated which in turnreduces or eliminates the fugitive gases generated through the action ofsuch a burner. These techniques also assist in managing the flow of theblister while it travels through the CBT.

In one embodiment of the first technique, the blister can be removedfrom the CBT through intermittent tapping. Under continuous operation,the level of the pool of blister and slag in the lower furnace ismaintained such that the flow of blister into the CBT is at the samerate as the flow of blister out of the CBT. One factor in maintainingthis balance is the removal of slag from the lower furnace. In thosecircumstances in which the production of blister is reduced due to areduction in feed to the furnace, or in those circumstances in whichdownstream processing makes a demand for more blister, or both, blistercan continue to flow temporarily from the CBT at or near the baselinerate (i.e. the rate prior to the change in circumstances) by allowingslag to accumulate in the lower furnace. This adds overburden to theblister in the lower furnace and in turn, this forces the blister levelin the CBT to rise.

In those circumstances in which the production of blister is increasedbeyond the capacity of downstream processing, or in those circumstancesin which the capacity of downstream processing is reduced, the blisterlevel in the CBT can be lowered by removing additional slag from thelower furnace. This reduces the overburden on the blister within thelower furnace, and this in turn allows for the accumulation of blisterwithin the lower furnace without causing a concommitent rise in theblister level in the CBT.

In effect, the process of this invention allows for intermittent tappingby allowing for the use of slag as a piston for raising and lowering thelevel of blister in the lower furnace which in turn influences directlythe level of blister in the CBT. The lower furnace and CBT form aU-tube, albeit with arms of different size, and an action on the levelof a fluid in one arm has a proportionate influence on the level offluid in the other arm. Continuous smelting and converting processesthat do not employ a furnace and/or CBT do not afford this level offlexibility in production scheduling.

Regardless the method of removing the blister copper, once removed it ischanneled by way of heated, covered launders either directly to anodefurnaces 47a and 47b, or to a holding furnace (not shown). Preferablythe anode refining furnaces are operated in such a manner that while oneis filling, the other is processing the blister copper to anode copper.The design and size of the anode furnaces can vary to conform to theoverall design of the smelting operation, but typically these are rotaryfurnaces sized such that when operated in tandem (i.e. in sequence),they can process the entire output of flash converting furnace 33without interruption. The rotary anode refining furnaces manufactured byKumera of Finland are exemplary.

In one embodiment of this invention, the blister copper is first routedto a holding furnace (not shown) in which it can simply be held in amolten state, or in which it can be further oxidized. Positioning, insequence if not in space, a holding furnace between the convertingfurnace and the anode furnaces imparts flexibility to the overallsmelting process by providing a location in which to store moltenblister copper in those circumstances in which the anode furnaces cannotaccept the blister for any reason, e.g. maintenance, upset, etc. Inaddition, the blister can be further processed in the holding furnace,to remove sulfur for example, which in turns either reduces the durationof or eliminates altogether the air blowing (oxidation) stage in theanode furnaces. Here too, the holding furnace is sized consistent withthe other equipment in the smelting operation, and it is of anyconventional design. In this embodiment, the holding furnace can beequipped with porous plugs to permit gas stirring while the blister issimply in a holding stage.

The blister is channeled to the anode furnaces by means of heated,covered launders in combination with a heated, covered divertor (FIGS.4a and 4b). Regardless of the source of the blister, i.e. the flashconverter or a holding furnace, the blister travels from the sourcethrough launder 48 to divertor 49 which is design to rotate aboutcentral axis 50 between launders 51a and 51b which in turn deliver theblister to furnaces 47a and 47b, respectively. Divertor 49 is equippedwith cover 52, and is lined with refractory 53. Divertor 49 is alsoequipped with a burner (not shown) for maintaining the blister in amolten state, and divertor 49 is mounted on turret 54 which allowsdivertor 49 to pivot between launders 51a and 51b. All the launders usedthroughout the smelting process, like the divertor, are linedappropriately with refractory, and covered or sealed against escape offugitive gases.

The anode furnaces are operated in conventional fashion. Upon filling,the blister is blown with oxygen or O₂ -enriched air, preferably throughmultiple tuyeres, such that the remaining sulfur values arequantitatively oxidized, and then the oxidized blister is reduced withconventional reagents such as one or more hydrocarbons in combinationwith air, ammonia alone or in combination with an inert gas such asnitrogen, and the like. During oxidation and reductin, the furnace isrotated such that the tuyeres (not shown) are positioned beneath thesurface of the blister. During reduction, the furnace may be rotatedback to its filling position, and the reducing agents sparged throughone or more porous plugs located in the lower surface of the furnace.Each furnace is equipped with at least one burner (not shown) typicallylocated at or near one end of the furnace and at or near its top wall.

In another embodiment of this invention, the anode furnace is designedfor continuous operation. The nonrotary furnace of this design (FIG. 5)is equipped with a dam 55 which divides the furnace basin into oxidationzone 56a and reduction zone 56b. Oxidation zone 56a is equipped withtuyeres 57a and 57b and overhead lances 58a and 58b for oxygen blowing,and porous plugs 59a and 59b for gas stirring. Reduction zone 56b isequipped with tuyeres 60a and 60b for introduction of reducing gases andoverhead burner 61 to maintain the blister at the desired temperature.Blister copper 62 moves from oxidation zone 56a to reduction zone 56b bythe continuous overflowing of dam 55 at a rate that is determined inlarge part by and is in registration with the rate at which blistercopper is introduced into oxidation zone 56a from launder 62 throughfeed port 63. Anode-grade copper is removed from reduction zone 56bthrough tapholes 64a and 64b at a similar rate. Gases and dusts exit thefurnace through port 65 for subsequent cleaning and processing. Thedesign of this furnace allows for continuous operation which eliminatesthe need for a second furnace.

After the blister is refined to anode copper (98% or greater copper), itis discharged from the anode furnace by conventional means, e.g.pouring, to anode casting wheel 66. This wheel, the Sumitomo rotarycasting wheel is exemplary, is designed to accommodate the sequentialoutput of both furnaces 47a and 47b, or the output of a single nonrotaryfurnace, without interruption of the anode furnace(s). In addition,wheel 66 is designed to accept anode copper from shaft furnace 67through holding furnace 68. The output from shaft furnace 67 is small ascompared to either of the anode refining furnaces and as such, theoutput is collected in holding furnace 68 until a sufficient amount hasbeen accumulated to justify transfer to the casting wheel. The source ofcopper for shaft furnace 67 is primarily recycled refinery scrap anodes,i.e. copper with a purity typically in excess of 98%). Anode copper 69is removed from wheel 66 at station 70 by conventional techniques.

Off-gases from both anode furnaces, the shaft furnace and all holdingfurnaces, as well as from the rotary dryer, launders, distribution dishand casting wheel, are collected by means not shown, and cleaned ofparticulate matter in high efficiency baghouses and/or scrubbersfollowed by desulferization in scrubbers. This combination of gascollection in combination with the flash smelting and convertingprocesses results in an extremely efficient control of emissions, insome embodiments with a capture rate in excess of 99% of fugitiveemissions, both particulate and gaseous.

In addition, the preferred embodiments of this invention, i.e. those inwhich high capacity flash furnaces are employed, produce very smallvolumes of process gas in the first instance. Preferably the flashfurnaces used in these embodiments operate with 70% oxygen enrichmentwhich in turn produces unusually high strength SO₂ gas. By way ofexample, a smelting furnace designed to process an average of 3,000tones per day of 28% copper concentrate will produce about 1,360 tonsper day of 70 percent copper matte. The gas volume from the smeltingfurnace is about 25,000 SCFM and from the converting furnace about11,000 SCFM, both containing 38% SO₂. The combined gas volume from thetwo furnaces is 36,000 SCFM which is lower than that produced from asingle Peirce Smith converter.

Although this invention has been described in considerable detail byreference to the drawings and assorted examples, this detail is forillustration only, and it is not to be construed as a limitation uponthe invention as described in the appended claims.

What is claimed is:
 1. A process for smelting copper concentratescontaining sulfur values to produce fire-refined blister copper as aprincipal product and slag and sulfur dioxide as by-products, theprocess comprising:A. melting and oxidizing the copper concentrate in asmelting furnace to produce molten matte, molten slag, and gaseoussulfur dioxide; B. removing the molten matte, molten slag and gaseoussulfur dioxide from the smelting furnace in separate streams; C.solidifying the molten matte; D. feeding the solidified matte into aconverting furnace in which the matte is converted to molten blistercopper, molten slag and gaseous sulfur dioxide; E. removing the moltenblister copper, molten slag and gaseous sulfur dioxide from theconverting furnace in separate streams; F. transferring the blistercopper from the converting furnace to an anode furnace through anarrangement of covered launders .[.and a covered divertor.].; and G.fire-refining the blister copper in the anode furnace to produce anodecopper and sulfur dioxide; the process conducted in a manner such thatless than about 2 percent of the sulfur values in the copper concentrateand less than about 5 kilograms per metric ton of copper of sulfurdioxide are released to the enviroment.
 2. The process of claim 1 inwhich the copper concentrate is melted and oxidized through the actionof a flash smelting furnace.
 3. The process of claim 2 in which themolten matte is removed from the smelting furnace through a taphole in asidewall of the furnace, and then transferred through a covered launderto solidification means.
 4. The process of claim 3 in which the moltenmatte is poured from the covered launder through a curtain of water toform granular, sand-like particles of matte.
 5. The process of claim 4in which the solid matte is transferred to and held in a storage areabefore used as a feed to the converting furnace.
 6. The process of claim5 in which the solid matte is dried and reduced in size to dust-likeparticles before fed to the converting furnace.
 7. The process of claim6 in which the solid matte is converted to blister copper through theaction of a flash converting furnace.
 8. The process of claim 7 in whichthe blister copper is removed from the converting furnace through acontinuous blister tapper which is in fluid communication with thefurnace.
 9. The process of claim 8 in which the blister copper is routedfrom the continuous blister tapper through the launder .[.anddivertor.]. arrangement.Iadd., into and through a divertor, .Iaddend.toone of two rotary anode furnaces operated in tandem.
 10. The process ofclaim 8 in which the blister copper is routed from the continuousblister tapper through a covered launder to a holding furnace in whichit is further oxidized before transfer through a launder and divertorarrangement to one of two rotary anode furnaces operated in tandem. 11.An apparatus for producing fire-refined blister copper as a principalproduct and slag and sulfur dioxide as by-products from copperconcentrates containing sulfur values, the apparatus comprising:A. aflash smelting furnace for melting and oxidizing copper concentrate toproduce molten matte, molten slag, and gaseous sulfur dioxide; B.solidification means for converting the molten matter into solid matte;C. covered launders for transferring the molten matte from the flashsmelting furnace to the solidification means; D. means for capturing thegaseous sulfur dioxide and processing it for use as a feed to an acidplant for the production of sulfuric acid; E. a flash converting furnacefor melting and oxidizing solidified matte to blister copper, moltenslag, and gaseous sulfur dioxide; F. means for transferring thesolidified matte to the flash converting furnace; G. an anode furnacefor fire-refining the blister copper to a quality suitable for casingcopper anodes; H. a covered launder .[.and divertor.]. arrangement fortransferring the blister copper from the flash converting furnace to theanode furnace; and I. means for capturing the gaseous sulfur dioxide andprocessing it for use as a feed to an acid plant for the production ofsulfuric acid.
 12. The apparatus of claim 11 further comprising meansfor drying and sizing the copper concentrate prior to its introductioninto the flash smelting furnace.
 13. The apparatus of claim 12 in whichthe drying means is a rotary kiln.
 14. The apparatus of claim 13 inwhich the solidification means is a water granulation apparatus.
 15. Theapparatus of claim 14 in which the means for capturing the gaseoussulfur dioxide includes a waste heat boiler, electrostatic precipitatorand a wet scrubber train.
 16. The apparatus of claim 15 furthercomprising pneumatic transfer means for transporting the solidifiedmatte from the water granulator to the storage area, and from thestorage area to the converting furnace.
 17. The apparatus of claim 16further comprising apparatus for drying and size reducing the solidifiedmatte before its use as a feed to the converting furnace.
 18. Theapparatus of claim 17 .Iadd.in which the covered launder arrangementincludes a diverter, and .Iaddend.in which the anode furnace comprisestwo rotary furnaces operated in tandem.
 19. The apparatus of claim 18further comprising a holding furnace positioned between the convertingfurnace and the anode furnace.
 20. The apparatus of claim 17 in whichthe anode furnace is a nonrotary furnace comprising an oxidation zoneand reduction zone, the zones divided by a dam.